This invention relates to a process and apparatus for upsetting pipe ends, in particular the pipe ends of drill rod pipes which form tool joints. The pipe end is held in a bottom die of a press and a shoulder mandrel is actually driven by the ram of the press into the pipe end thereby simultaneously upsetting the pipe end and filling the free space between the bottom die and the pipe end.
Processes and apparatuses of this type are already known. For example in German published application No. 2629796 an hydraulic press of this type is described. In this known hydraulic pipe end-forming machine pipe ends can be upset outwardly or inwardly. However, in swaging the pipe end inwardly difficulties arise, in particular with respect to obtaining a precisely defined transition region between the upset pipe section and the not yet deformed pipe end. Such defined transition regions in pipe ends of the aforedescribed type are, however, essential for drill string pipes with pipe joints, which are standardized with both an inward as well as an outward upset as well as a combination of both.
According to another known process the pipe ends are heated over the length representing a deformation region by different means to a hot forming temperature. The thus heated end is then fed into a mechanical or hydraulic forming machine which is provided with a clamping tool that encloses the pipe end in the forming region. This known device includes an upsetting mandrel the pin of which has a diameter which correspondes to the internal diameter of the pipe end to be upset. The shoulder diameter of the mandrel corresponds to the external diameter of the pipe. This mandrel is driven by means of a hydraulically actuated ram or piston-cylinder unit into the exterior forming-shaping tool. Due to the restricted free space between the shaping tool and the mandrel, the pipe end is upset inwardly so that an internal step is produced in the pipe end. Since the mandrel must be retracted oppositely to the upsetting direction, it is impossible in this case to forge a defined transition region between the original pipe and the upsetted pipe end. In view of the large difference in wall thickness between the undeformed pipe and the upset pipe end there is produced a transition zone which extends over a larger region of the pipe length and the contour of which is ill-defined.
The upsetting process of the state of the art is carried out, independent of the increasing desired wall thickness, in one or several stages. Thus, after a second heating step, the exterior of the pipe end is deformed in additional deforming stations outwardly with suitable tools in a manner analogous to the inward upsetting steps. Since in these known processes the external forming tools act simultaneously as clamping tools, which are constructed as a multi-membered tool, and further in view of the fact that the pipe tolerances for the diameter affect the clamping stroke of the outer die, substantial ridges or fins are produced in this forming process.